For the past 35 years, the annual Richard Tucker Award has been granted to an American singer poised on the edge of a major national and international career, with a list of winners that reads like a who’s who of international opera stars. This year’s recipient, mezzo-soprano Isabel Leonard, has been called “opera’s new ‘it girl,'” and some of her 2013-14 season highlights include Così fan tutte at The Metropolitan Opera (Dorabella); The Barber of Seville at San Francisco Opera and Dallas Opera (Rosina); and the Marilyn Horne 80th Birthday Celebration at Carnegie Hall.